(a) Field of the Disclosure
The present disclosure relates to automatic transmissions for vehicles. More particularly, the present disclosure relates to a planetary gear train of an automatic transmission for a vehicle.
(b) Description of the Related Art
Recently, increasing oil prices have caused vehicle manufactures all over the world to rush into infinite competition. Particularly in the case of engines, manufactures have been pursuing efforts to reduce the weight and improve fuel efficiency of vehicles by reducing engine size and the like.
As a result, research into weight reduction and fuel efficiency enhancement through downsizing has been conducted in the field of engines. Research has also been conducted for simultaneously securing operability and fuel efficiency competitiveness through multiple speed stages in the field of automatic transmissions.
However, in an automatic transmission, as the number of speed stages increases, the number of internal components also increases. As a result, the automatic transmission may be difficult to mount, the manufacturing cost and weight may be increased, and power transmission efficiency may be deteriorated.
In recent years, 8-speed automatic transmissions have been implemented. Research and development of a planetary gear train capable of implementing more speed stages have also been actively conducted.
A conventional automatic transmission of eight or more speed stages typically includes three or four planetary gear sets and five or six control elements (frictional elements). Thus, mountability may deteriorate due to an increase in volume and weight of the transmission.
In this regard, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements have been attempted. However, such arrangements are not widely applicable, and using the dog clutches may deteriorate shift-feel.
The above information disclosed in this Background section is only to enhance understanding of the background of the disclosure. Therefore, the background may contain information that is not prior art that is already known in this country to a person of ordinary skill in the art.